1. Field of the Invention
The present invention relates to a multi-color image-forming medium which is constituted such that at least two colors are developed to form a multi-color image.
2. Description of the Related Art
As a conventional type of multi-color image-forming medium, there is known a heat-sensitive color-developing sheet, which is constituted such that at least two colors can be developed. In general, such a heat-sensitive color-developing sheet comprises a sheet of paper coated with a heat-sensitive color-developing layer containing at least two kinds of leuco-pigment components and a color developer component. As is well known, a leuco-pigment per se exhibits no color. Namely, usually, the leuco-pigment exhibits milky-white or transparency, and reacts with the color developer, to thereby produce a given single-color (e.g. magenta, cyan or yellow). The leuco-pigment components, contained in the color-developing layer, feature different color-developing temperatures such that different colors can be obtained at the respective color-developing temperatures.
For example, when the leuco-pigment components, contained in the color-developing layer, are composed of respective magenta- and and cyan-developing leuco-pigments featuring low and high color-developing temperatures, respective magenta and blue can be obtained at the low and high color-developing temperatures thereof. Namely, when a first temperature between the low magenta-developing temperature and the high cyan-developing temperatures is locally exerted on the color-developing layer, only the magenta-developing leuco-pigment component reacts with the color developer component so that magenta is developed at the localized area where the first temperature is exerted. Also, when a second temperature, higher than the high cyan-developing temperature, is locally exerted on the color-developing layer, both the magenta- and cyan-developing leuco-pigment components react with the color developer component so that blue is developed as a mixture of magenta and cyan at the localized area where the second temperature is exerted.
As is apparent from the aforesaid example, it is impossible to independently develop cyan by the cyan-developing leuco-pigment component. Thus, the conventional multi-color image-forming medium is inferior in efficiency of color development, as it is possible to only independently develop a leuco-pigment component exhibiting the lowest color-developing temperature.
Also, in the aforesaid example, the temperature difference between the low magenta-developing temperature and the high cyan-developing temperature must be sufficiently high, before development of pure magenta can be obtained on the color-developing layer. Namely, if the temperature difference between the magenta-developing temperature and the cyan-developing temperatures is too low, a part of the cyan-developing leuco-pigment component may undesirably react with the color developer component at the first temperature for the development of magenta, resulting in the development of magenta with a cyan tint.
Further, in the aforesaid example, the low magenta-developing temperature must be more than 100xc2x0 C., before erroneous and accidental development of magenta can be prevented, because the color-developing layer may be frequently exposed to, for example, a temperature in a range of 80 to 100xc2x0 C. under ordinary circumstances. Thus, if the low magenta-developing temperature is less than 100xc2x0 C., the erroneous and accidental development of magenta may often occur.
Accordingly, in the conventional multi-color image-forming medium, a combination of different leuco-pigments, which can be utilized to form a heat-sensitive color-developing layer, is severely and considerably restricted, because respective various leuco-pigments feature inherent color-developing temperatures. In the aforesaid example, if one is optionally selected from among various magenta-developing leuco-pigments, it cannot be ensured that there is a cyan-developing leuco-pigment which can be combined with the selected magenta-developing leuco-pigment.
Conventionally, although a user frequently requires that only one single-color is developed with a desired tone in a multi-color image-forming medium, it is virtually impossible to even obtain the development of only the single-color with the desired tone, because of the severe and considerable restriction of the combination of different leuco-pigments.
Further, the conventional multi-color image-forming medium is inferior in thermal energy efficiency, because the lowest color-developing temperature must be more than 100xc2x0 C. so that erroneous and accidental development of color is prevented, and because the difference between the low color-developing temperature and the high color-developing temperature must be high.
Furthermore, in the conventional multi-color image-forming medium, of course, it is impossible to utilize a pigment type other than a leuco-pigment.
Therefore, an object of the present invention is to provide a multi-color image-forming medium which is constituted such that development of only one single-color with a desired tone can be ensured.
Another object of the present invention is to provide a multi-color image-forming medium of the aforesaid type, which features superior efficiency for development of colors and superior thermal energy efficiency.
In accordance with a first aspect of the present invention, there is provided a multi-color image-forming medium which comprises a substrate, and a color-developing layer coated on the substrate. The color-developing layer is formed as a heat-sensitive color-developing layer containing a plurality of pressure-sensitive microcapsules uniformly distributed therein. Each of the microcapsules is filled with a dye exhibiting a first single-color, and features a pressure characteristic to be physically broken when being subjected to a predetermined pressure. The heat-sensitive color-developing layer features a thermal characteristic to be molten when being subjected to a first temperature, which is preferably less than 100xc2x0 C., so that the microcapsules can be directly subjected to the predetermined pressure. Further, the heat-sensitive color-developing layer features a color-developing characteristic to develop a second single-color when being subjected to a second temperature more than the first temperature.
The heat-sensitive color-developing layer may be composed of a first leuco-pigment component, and a color developer component for the first leuco-pigment component. The color developer component is thermally molten under at least the first temperature, and the first leuco-pigment component reacts with the color developer component, thereby developing the second single-color under at least the second temperature. The heat-sensitive color-developing layer may contain a sensitizer component that regulates a color-developing temperature of the leuco-pigment component such that the leuco-pigment component reacts with the color developer component under at least the second temperature. The heat-sensitive color-developing layer may further contain a second leuco-pigment component which reacts with the color developer component, thereby developing a third single-color under at least a third temperature more than the second temperature.
Optionally, the heat-sensitive color-developing layer may be composed of a first type of heat-sensitive microcapsule filled with a first leuco-pigment, and a color developer component for the first leuco-pigment. The color developer component is molten under at least the first temperature, and the first type of heat-sensitive microcapsule featuring a thermal characteristic to be thermally broken when being subjected to at least the second temperature. The first leuco-pigment reacts with the color developer component, thereby developing the second single-color under at least the second temperature. The heat-sensitive color-developing layer may contain a sensitizer component that regulates a color-developing temperature of the first leuco-pigment such that the first leuco-pigment reacts with the color developer component under at least the second temperature. The heat-sensitive color-developing layer may further contain a second type of heat-sensitive microcapsule filled with a second leuco-pigment, and the second type of heat-sensitive microcapsule features a thermal characteristic to be thermally broken when being subjected to at least a third temperature more than the second temperature. The second leuco-pigment reacts with the color developer component, thereby developing a third single-color under at least the third temperature.
In accordance with a second aspect of the present invention, there is provided a multi-color image-forming medium which comprises a substrate, a pressure/heat-sensitive color-developing layer coated on the substrate and containing a plurality of pressure-sensitive microcapsules uniformly distributed therein. Each microcapsule is filled with a dye exhibiting a first single-color, and features a pressure characteristic to be broken when being subjected to a predetermined pressure. The image-forming medium further comprise a first heat-sensitive color-developing layer coated on the pressure/heat-sensitive color-developing layer. The pressure/heat-sensitive color-developing layer is composed of a binder component for the pressure-sensitive microcapsules, and the binder component features a thermal characteristic to be thermally molten when being subjected to a first temperature, which is preferably less than 100xc2x0 C., so that the microcapsules can be directly subjected to the predetermined pressure. The first heat-sensitive color-developing layer features a color-developing characteristic to develop a second single-color when being subjected to a second temperature more than the first temperature.
The first heat-sensitive color-developing layer may be composed of a first leuco-pigment component, and a color developer component for the first leuco-pigment component, and the color developer component is thermally molten under at least the first temperature. The first leuco-pigment component reacts with the color developer component, thereby developing the second single-color under at least the second temperature. The first heat-sensitive color-developing layer may contain a sensitizer component that regulates a color-developing temperature of the first leuco-pigment component such that the first leuco-pigment component reacts with the color developer component under at least the second temperature.
In the second aspect of the present invention, the image-forming medium may further comprise a second heat-sensitive color-developing layer coated on the first heat-sensitive color-developing layer, and the second heat-sensitive color-developing layer feature a color-developing characteristic to develop a third single-color when being subjected to a third temperature more than the first temperature but less than the second temperature.
The first heat-sensitive color-developing layer may be composed of a first leuco-pigment component, and a color developer component for the first leuco-pigment component. The color developer component is molten under at least the first temperature, the first leuco-pigment component reacts with the color developer component, thereby developing the second single-color under at least the second temperature. Also, the second heat-sensitive color-developing layer may be composed of a second leuco-pigment component, and a color developer component for the second leuco-pigment component. The color developer component is molten under at least the first temperature, and the second leuco-pigment component reacts with the color developer component, thereby developing the third single-color under at least the third temperature.
The first heat-sensitive color-developing layer may contain a first sensitizer component that regulates a color-developing temperature of the first leuco-pigment component such that the first leuco-pigment component reacts with the color developer component under at least the second temperature. Also, the second heat-sensitive color-developing layer may contain a second sensitizer component that regulates a color-developing temperature of the second leuco-pigment component such that the second leuco-pigment component reacts with the color developer component under at least the third temperature.
Optionally, a boundary layer may be interposed between the pressure/heat-sensitive color-developing layer and the first heat-sensitive color-developing layer to thereby prevent a dye, discharged from a broken pressure-sensitive microcapsule, from being in contact with the first heat-sensitive color-developing layer.
In the second aspect of the present invention, the multi-color image-forming medium may further comprises a second heat-sensitive color-developing layer interposed between the pressure/heat-sensitive color-developing layer and the first heat-sensitive color-developing layer, and the second heat-sensitive color-developing layer features a color-developing characteristic to develop a third single-color when being subjected to a third temperature more than the first temperature but less than the second temperature. The second heat-sensitive color-developing layer also may be composed of a second leuco-pigment component, and a color developer component for the second leuco-pigment component. The color developer component is molten under at least the first temperature, and the second leuco-pigment component reacting with the color developer component, thereby developing the third single-color under at least the third temperature.
Optionally, the first heat-sensitive color-developing layer may be composed of a first type heat-sensitive microcapsule filled with a first leuco-pigment, and a color developer component for the first leuco-pigment component. The color developer component is molten under at least the first temperature, and the first type of heat-sensitive microcapsule features a thermal characteristic to be thermally broken when being subjected to at least the second temperature. The first leuco-pigment reacts with the color developer component, thereby developing the second single-color under at least the second temperature.
Similarly, the second heat-sensitive color-developing layer may be composed of a second type heat-sensitive microcapsule filled with a second leuco-pigment, and a color developer component for the second leuco-pigment component. The color developer component is molten under at least the first temperature, and the second type of heat-sensitive microcapsule features a thermal characteristic to be thermally broken when being subjected to at east the third temperature. The third leuco-pigment reacts with the color developer component, thereby developing the third single-color under at least the third temperature.